High-molecular weight conjugates obtained by bonding physiologically active substances such as an anticancer agent or an anti-inflammatory agent, especially a physiologically active substances with low solubility in water, to a high-molecular weight carrier have been studied extensively since the high-molecular weight conjugates improve the in vivo pharmacokinetics of the physiologically active substances themselves, the water solubility thereof and the like, and are expected to thus improve the efficacy of the substances as drugs. Particularly block copolymers in which a hydrophilic polymer and a hydrophobic polymer are bonded are characterized by being capable of maintaining the water solubility as the whole polymer even if the amount of a physiologically active substances carried thereon is increased, by forming a micelle having the hydrophobic polymer carrying the physiologically active substances as the inner shell and the hydrophilic polymer covering the surface.
Patent Document 1 discloses a compound in which a drug is bonded to a block copolymer of a polyethylene glycol and a polyaspartic acid and which forms micelles and has water solubility. Patent Document 2 discloses a high-molecular weight derivative of camptothecins in which a side chain carboxy group of a block copolymer of a polyethylene glycol and a polyglutamic acid is bonded to a phenolic hydroxyl group of the camptothecins.
Patent Document 3 discloses a compound in which a drug is bonded to a polyethylene glycol through a specific linker to cause a benzyl elimination reaction. Patent Document 4 discloses a compound in which a drug is bonded to a branched amino acid such as aspartic acid bonded to a polyethylene glycol, through a specific linker to cause a benzyl elimination reaction.    Patent Document 1: Japanese Patent No. 2694923    Patent Document 2: WO 2004/39869    Patent Document 3: Japanese Patent Application Laid-Open Publication (Kohyo) No. 2002-508400    Patent Document 4: Japanese Patent Application Laid-Open Publication (Kohyo) No. 2004-532289